CGS60 - Stomp Box Adaptor (V2.0)

Ken Stone's Stomp Box Adaptor can be used as an external input amplifier, a way to use effects pedals with synthesizer signal levels, or a way to use synthesizer modules with instruments such as electric guitars.

Details

Details

This is a new version of the Stomp Box Adapter. This time there is no provision for any jacks on the PCB. It can be used as an external input amplifier, a way to use effects pedals with synthesizer signal levels, or a way to use synthesizer modules with instruments such as electric guitars.

A little on how it works:

The schematic of the Stomp Box Adapter. The jacks shown on the diagram are for connection to the stomp-box. Note that the switching contact on the input jack is connected to 0V.

Modular synthesizers generally use much higher signal levels than are used in effects pedals, so directly connection the two will create two problems. First, the excessive signal will cause the input of the effects pedal to overload/distort. Second, the output from effects pedal is too weak to drive synthesizer modules without some amplification. To compensate for these problems, the signal from the synthesizer must be dropped to a fraction of what it was, while the output of the effects pedal must be amplified by the same amount to restore it to a level suitable for the synthesizer. I have chosen to use a ratio of 20 as this encompases the signal levels of many synths. If you know for certain that the ratio is too great, the ratio can be reduced to reduce the amplification of any effects pedal noise. For example, if an effects pedal works on a 1V p-p signal, and a synthesizer has a maximum output of 5V p-p, a ratio of 5 would be adequate.

The preamplifier of the stomp box adapter is a basic non-inverting amplifier with an AC gain of 20, and suppression capacitors as needed. The input impedance is approximately 150k. The AC gain can be reduced if need by by increasing the value of the 470R resistor. For example, a 1k resistor in this position would give a gain of 10. The 1k resistor of the input divider would need to be increased to 2k2 to keep the drop and gain matched.